Process for reversed planographic printing



United States Patent Int. Cl: 009d 11/12 US. Cl. 106-31 4 Claims The present invention relates to a printing ink, more particularly to a printing ink for planographic printing.

The fact that a greasy image on an otherwise nongreasy surface can be selectively wetted by a greasy ink forms the bases of all clasical lithographic or planographic printing processes. Thus, the classical planographic inks are constituted by a lipophilic phase wherein pigments and other suitable ink ingredients are worked up and which does not absorb water or only to a small extent. During printing according to the classical planographic process the printing plate is kept supplied with an aqueous composition so as to keep the non-printing areas sufiiciently hydrophilic. This method of printing thus requires in addition to an inking system a so-called damping system in order to keep the hydrophilic areas covered with water or a colourless aqueous composition.

Recently a planographic printing process has been developed wherein use is made of a printing ink the coloured medium of which is an aqueous ink composition and a damping system is used to cover the oleophilic areas of the printing master with a colourless oleophilic liquid composition. This printing process, which is called reversed planographic printing process is very suitable for direct planographic printing, in other words a process wherein there is no need for an intermediate cylinder with rubber blanket.

The present invention provides an ink that can be used in a reversed planographic printing process to wet selectively a hydrophilic image On an otherwise non-hydrophilic or less hydrophilic surface and which enables a damping system to be dispensed with. The ink is very suitable for use in a planographic printing apparatus having a direct inking roller system.

A printing ink according to the invention comprises a coloured printing medium (coloured here includes black) in the form of a hydrophilic more particularly an aqueous composition, and a lipophilic phase which is colourless or substantially colourless or of a contrasting colour or tone is dispersed in the hydrophilic phase. For most purposes, the lipophilic phase will require to be colourless and it will hereafter be referred to as such but it will be understood that absence of colour in the lipophilic phase is not critical for the performance of the invention and that some colour in this phase is permissible provided that a sufficient visible differentiation is obtained as between the printing image areas and the nonprinting image areas of the plate when the ink is applied. The term relatively uncolored will be employed to denote either of these possibilities.

On contact with a printing master which is image-wise differentiated into hydrophilic and hydrophobic areas, the colourless lipophilic phase readily separates out from the hydrophilic phase wherein it is emulsified, thus enabling the selective deposition and spreading out of the coloured hydrophilic phase on the hydrophilic areas.

For obtaining the requiredresults, certain organic solvents which are immiscible with water or substantially so have proved to be very suitable constituents for forming the lipophilic phase of the ink. Such solvents belong to the groups: aliphatic hydrocarbon compounds, cyclo- Patented May 19, 1970 aliphatic hydrocarbon compounds and aliphatically substituted aromatic compounds. Preferably a hydrocarbon compound is used which is a liquid at room temperature. The selected compound should not have too high a viscosity nor too high a vapour pressure. As regards this latter requirement n-hexane has been found to be not very suitable. Compounds which can be used instead of the said hydrocarbon compounds but which do not give equally good results are aliphatic esters having suflicient water-resistance e.g. arnyl acetate. As the lipophilic phase it is preferable to use a water-immiscible liquid having a boiling point above C.: e.g. white spirit having a boiling range of from C. to 200 C., parafiin oil, xylene, cumene, cymene, tetrahydronaphthalene, and decahydronaphthalene. Two or more different water-immiscible liquids may be used as the lipophilic phase if desired.

Depending on the type of lipophilic liquid applied the ratio of hydrophilic phase to lipophilic phase is prefer ably from 4:1 to 1:1 by weight.

The lipophilic phase may contain indissolved state hydrophobic substances such as silicone, paraflin, hydrophobic polymers and copolymers, waxes and any other fatty substance that improve the water-repellency.

The coloured hydrophilic phase contains water and/ or a highly hydrophilic liquid as the most important liquid ingredient, and a certain amount of pigment as the most important solid ingredient to produce a sufiiciently dense coloured visible print. The pigment may be of the organic or inorganic type but must be insoluble in the lipophilic phase dispersed in the ink. Particulars about commonly used printing ink pigments can be found in Practical Printing and Binding by Harry Whetton, Odhams Press Limited, Long Aere, London, W.C. 2 (1946), pp. 346-350.

The Water-insoluble pigments can be first dispersed in the hydrophilic phase before mixing the latter with the lipophilic one. For obtaining a stable dispersion of the pigments hydrophilic protective colloids and/or Wetting agents may be used.

Aqueous carbon black dispersions that contain up to 60% of carbon black are preferably used for obtaining black prints.

In addition to pigments and dispersing agents the hydrophilic phase of the ink preferably also contains ingredients which prevent the ink from drying too fast, more particularly which prevent the ink from drying on the inking rollers. As examples of such ingredients may be mentioned water-attracting compounds e.g. magnesium chloride, zinc chloride, lithium chloride and polyhydroxy compounds such as hexane diol.

To improve the fastness to erasure, water-soluble polymeric compounds or pre-condensates, preferably polymers which harden or further polymerize during the drying of the ink can be incorporated into the hydrophilic phase. Compounds improving the fastness to erasure are e.g. water-soluble polyethylene glycol and derivatives, gum arabic, zein, water-soluble cellulose derivatives, polyvinyl alcohol, water-soluble starch derivatives and water-soluble condensation products of formaldehyde with urea, modified ureas, melamine and modified melamines known in paper and textile treatment. Especially good results are obtained with copoly(vinyl acetate/crotonic acid) (95/5). For improving the fastness to erasure hydrophobic thermoplastic film-forming polymers and copolymers may be added to the hydrophilic, preferably aqueous phase as a dispersion or latex. Good results are obtained with an aqueous dispersion of a copolymer of butyl acrylate and vinyl acetate.

A printing ink according to the present invention is preferably prepared by mixing together in a ball-mill or other suitable mixing apparatus the hydrophilic phase containing its proper ingredients, and the lipophilic phase. The content of dispersed pigment in the hydrophilic phase is preferably so high that a paste-like composition is obtained which can however still be readily distributed between the inking rollers.

Printing plates suitable for use in conjunction with a printing ink according to the present invention need not possess a better hydrophilic-hydrophobic image differentiation than the printing plates used in conventional planographic printing. Accordingly, a sufficient imagewise hydrophobic-hydrophilic differentiation may be achieved by every known technique capable of producing useful results in conventional planographic printing. If positive copies are to be printed, the printing image areas are the hydrophilic areas and the non-printing image areas are the hydrophobic i.e. grease-accepting areas.

Printing inks according to the invention show particular advantage when applied to printing plates of which the printing image areas (i.e. the hydrophilic or more hydrophilic areas) are at least to some extent waterpermeable. Information about plates having such a characteristic and about their preparation is to be found in the specifications found in US. patent application 421,861 which is a continuation-in-part application to U.S. patent application 337,664. In particular, US. patent application 421,861 describes a thermographic process for creating an image-wise hydrophilic-hydrophobic differentiation, which is very suitable for rapidly producing planographic printing plates of good quality which can be inked with a printing ink according to the invention.

By way of example suitable printing plates can also be prepared rapidly by application of the silver complex diffusion transfer process as described in British patent specification 913,591 and Canadian patent specification 658,050 or by application of an electrophotographic process. As examples of electrophotographic processes of preparing printing plates, we refer to US. Pats. 2,952,536 and 3,001,872. The specifications of the patents and particularly the specifications of the co-pending applications above referred to should be read in conjunction with the present specification.

The expression printing plate as used in the present specification is used broadly to denote any printing element with printing and non-printing areas exhibiting hydrophilic and hydrophobic properties respectively (or exhibiting substantially different hydrophilicity or hydrophobicity) and capable of use in a planographic printing process. The expression thus includes both rigid or substantially rigid elements and flexible elements.

The following examples illustrate the present invention.

EXAMPLE 1 75 g. of a carbon black dispersion containing per 100 g. 53 g. of carbon black, 23 g. of Water, 18 g. ofglycol and 6 g. of nonylphenyl polyethylene oxide (containing 15 ethylene oxide units) are mixed with 225 g. of a 20% aqueous solution of cellulose acetophthalate (DS acetyl 1.3 to 1.5, DS phthalyl 0.9 to 1.2, having measured at 20 C. a viscosity of 12 cps. as a 3% solution in a mixture of 35 cc. of methylglycol, 60 cc. of ethanol and 5 cc. of acetone), g. of magnesium chloride and 10 g. of hexanediol. While strongly stirring a mixture of 110 g. of white spirit (boiling range: 140-200" C.) and 3 0 g. of xylene are added to the first mixture. In the paste obmined the dispersion of the oleophilic phase in the aqueous phase remains stable. Yet, when rubbing with said paste a planographic printing plate, that possesses an image-wise hydrophilic-hydrophobic differentiation, only the aqueous phase settles down on the hydrophilic areas.

EXAMPLE 2 To 75 g. of Permanent Schwarz P. R. Colanyl Neu (trade name for a stable aqueous carbon black dispersion marketed by Farbwerke Hoechst A.G. Frankfurt am Main- Hochst, Germany) are added 5 g. of a 53% aqueous dispersion of copoly(butyl acrylate/vinyl acetate) (/50), 10 g. of magnesium chloride and 10 g. of hexanediol. To this mixture is added whilst effectively stirring a mixture of g. of white spirit (boiling range 140-200 C.) and 10 g. of xylene. The paste obtained is stable on storage for Weeks. Yet, when rubbing a planographic printing plate, that shows an image-wise hydrophobic-hydrophilic differentiation, with said plaste only the aqueous phase settles down on the hydrophilic areas.

An equally good selective adsorption of the aqueous phase can be realized by substituting for the above quantity of white spirit amounts varying from 25 to g. or otherwise by replacing the mixture of 60 g. of white spirit and 10' g. of xylene used by one of the following liquids or mixtures:

50 g. of white spirit,

40 g. of xylene,

50 g. of paraffinic oil,

50 g. of decahydronaphthalene,

50 g. of decahydronaphthalene and 10 g. of xylene.

EXAMPLE 3 To 75 g. of an aqueous carbon black dispersion as described in Example 2 are added 20 g. of an aqueous solution of a malamine-formaldehyde resin, g. of a 30% aqueous solution of a copoly(vinyl acetate/ crotonic acid ammonium salt) (95/5), and 10 g. of hexanediol. To this mixture 80 g. of white spirit and 10 g. of xylene are added and the whole is effectively mixed by means of an ultra-sonic mixing apparatus.

EXAMPLE 4 75 g. of an aqueous carbon black dispersion as described in Example 1 are mixed with g. of a 30% aqueous solution of a copoly(vinyl acetate/crotonic acid ammonium salt) (95/5) and 10 g. of hexanediol. The whole is homogeneously mixed with 70 g. of white spirit (boiling range 200 C.) and 40 g. of Xylene by stirring effectively.

EXAMPLE 5 In a ball-mill 20 g. of carbon black having a particle size of 0.1/L are mixed with 85 g. of water, 25 g. of casein and 20 g. of hexanediol. Once a homogeneous dispersion is obtained 100 g. of white spirit and 10 g. of xylene are admixed.

EXAMPLE 6 10 g. of carbon black having a particle size of 0.1 to 0.4;1. are homogeneously mixed with 25 g. of water, 25 g. of a 20% aqueous solution of cellulose acetophthalate of the type as described in Example 1 and 10 g. of hexanediol. To the mixture obtained 50 g. of white spirit and 10 g. of xylene are added and intimately mixed therewith.

EXAMPLE 7 10 g. of carbon black having an average particle size of 0.020,u are thoroughly mixed with 50 g. of a 10% aqueous solution of a vinyl polymer (containing 100% of vinyl alcohol units) and 10 g. of hexanediol. The dispersion obtained is homogeneously mixed with a mixture of 50 g. of white spirit and 10 g. of xylene.

EXAMPLE 8 10 g. of a green pigment: Pigment Green B (C.I. 10,006) are mixed with 50 g. of a 10% aqueous solution of polyvinyl alcohol and 10 g. of hexanediol. Once a homogeneous mixture is obtained 50 g. of white spirit and 10 g. of xylene are added and emulsified therein.

EXAMPLE 9 To 75 g. of Permanent Schwarz P. R. Colanyl Neu (trade name for a stable carbon black dispersion marketed by Farbwerke Hoechst A.G. Frankfurt am Main-Hochst, Germany) are added 7 g. of a 50% aqueous dispersion of polyvinyl propion-ate, g. of magnesium chloride and 10 g. of hexanediol. To this mixture is added While eifectively stirring a mixture of 60 g. of white spirit (boiling range 180200 C.) and 10 g. of Xylene. The paste obtained is stable on storage. Yet when brought by means of an inking roller on the planographic printing master which is braced on the impression cylinder of a rotary printing machine only the aqueous phase settles and spreads out on the hydrophilic areas.

An equally good result is obtained when in the ink the aqueous dispersion of polyvinyl propionate is substituted for a same amount of a 50% aqueous dispersion of copoly (ethyl acrylate/vinylmethyl ether) (80/20) which contains 5% of polyvinyl alcohol.

EXAMPLE 1O 13 g. of zein are dissolved in 26 g. of triethylene glycol by heating at 45 C. with stirring. To this solution are added while vigorously being stirred 75 g. of the dispersion of carbon black described in Example 1. To this mixture is added still with vigorous stirring a solution of g. of parafiinic oil in 70 g. of white spirit.

What we claim is:

1. An improved reversed planographic printing process wherein the improvement comprises inking the planographic printing form with an oil-in-water emulsion ink composition consisting essentially of a relatively uncolored lipophilic liquid dispersed phase emulsified in a hydrophilic aqueous liquid continuous phase, said continuous phase consisting essentially of water, a dispersing agent and a pigment insoluble in said lipophilic phase, said lipophilic phase consisting essentially of a natural or synthetic hydrophobic material selected from the group consisting of oils, waxes, and resins dissolved in at least one organic water-immiscible liquid solvent selected from the group consisting of aliphatic hydrocarbons, cycloaliphatic hydrocarbons, aliphatically substituted aromatic hydrocarbons and aliphatic esters, said solvent having a vapor pressure lower than n-hexane and a boiling point above C., the weight ratio of said hydrophilic phase to said lipophilic phase being from 4:1 to, 1:1, said lipophilic phase remaining stably dispersed in said hydrophilic continuous phase until the ink composition is contacted with the printing form and then separating therefrom.

2. The process of claim 1 wherein the hydrophilic aqueous liquid continuous phase also includes a waterattracting material selected from the group consisting of magnesium chloride, zinc chloride, lithium chloride and hexane diol.

3. The reversed planographic printing process of claim 1 wherein said pigment is present therein in such an amount that the ink composition has a paste-like consistency.

4. The reversed planographic printing process of claim 1 wherein carbon black is dispersed in the hydrophilic liquid phase.

References Cited UNITED STATES PATENTS 3,043,784 7/ 1962 Remer 10632 XR 3,086,873 4/1963 Steinbrunner l06-32 XR 3,129,176 4/1964 Ihde 106-20 XR 3,199,991 8/1965 Schelling et a1 10632 OTHER REFERENCES Ellis: Printing Inks, N.Y., Reinhold Pub. Corp., 1940, pp. 345-9.

JULIUS FROME, Primary Examiner I. B. EVANS, Assistant Examiner US. Cl. X.R. 

1. AN IMPROVED REVERSED PLANOGRAPHIC PRINTING PROCESS WHEREIN THE IMPROVEMENT COMPRISES INKING THE PLANOGRAPHIC PRINTING FORM WITH AN OIL-IN-WATER EMULSION INK COMPOSITION CONSISTING ESSENTIALLY OF A RELATIVELY UNCOLORED LIPOPHILIC LIQUID DISPERSED PHASE EMULSIFIED IN A HYDROPHILIC AQUEOUS LIQUIS CONTINUOUS PHASE, SAID CONTINUOUS PHASE CONSISTING ESSENTIALLY OF WATER, A DISPERSING AGENT AND A PIGMENT INSOLUBLE IN SAID LIPOPHILIC PHASE, SAID LIPOPHILIC PHASE CONSISTING ESSENTIALLY OF A NATURAL OR SYNTHETIC HYDROPHOBIC MATERIAL SELECTEDK FROM THE GROUP CONSISTING OF OILS, WAXES, AND RESINS DISSOLVED IN AT LEAST ONE ORGANIC WATER-IMMISCIBLE LIQUID SOLVENT SELECTED FROM THE GROUP CONSISTING OF ALIPHATIC HYDROCARBONS, CYCLOALIPHATIC HYDROCARBONS, ALIPHATICALLY SUBSTITUTED AROMATIC HYDROCARBONS AND ALIPHATIC ESTERS, SAID SOLVENT HAVING A VAPOR PRESSURE LOWER THAN N-HEXANE AND A BOILING POINT ABOVE 100*C., THE WEIGHT RATIO OF SAID HYDROPHILIC PHASE TO SAID LOPOPHILIC PHASE BEING FROM 4:1 TO 1:1, SAID LIPOPHILIC PHASE REMAINING STABLE DISPERSED IN SAID HYDROPHILIC CONTINUOUS PHASE UNTIL THE INK COMPOSITION IS CONTACTED WITH THE PRINTING FORM AND THEN SEPARATING THEREFROM. 